PROJECT SUMMARY ? Project 5 Chronic stress has devastating effects on brain function and mental health. The traditional view holds that this results solely from the effects of stress on neurons, but recently a richer picture has emerged that implicates direct effects of stress on the cerebral vasculature. Understanding this impact of stress on the circulation may reveal new treatments for stress-related brain dysfunction. Our prior work demonstrated that chronic stress drastically impairs the function of the small penetrating cerebral arteries that feed the brains capillary bed. Perturbation of brain blood flow through this mechanism may in turn precipitate neuronal dysfunction. However, because capillaries are in close apposition with all neurons and vastly outmatch the reach of penetrating arterioles, it is likely that stress has an even more profound disruptive effect on capillary function. Our overarching goal is to understand how chronic stress alters capillary control of brain blood flow, and how these deficits can be corrected. To accomplish this, we will pursue two primary objectives: i) to elucidate the mechanisms by which capillaries sense and respond to neural activity to tune blood flow and, ii) to determine the mechanisms through which chronic stress disrupts this interaction. To this end, we propose the following specific aims: Aim 1. To elucidate the relationship between neuronal activity and capillary calcium (Ca2+) signaling in the brain in vivo. Our preliminary data suggest that capillary endothelial cell (cEC) Ca2+ signals are entrained to neuronal activity. Here, we will use a novel transgenic mouse line to characterize the relationship between neuronal activity and capillary Ca2+ signaling. Aim 2. To elucidate the Ca2+-dependent signaling mechanisms that translate neuronal activity into changes in capillary blood flow. Our preliminary data support the concept that neuronally-evoked capillary Ca2+ signals control local cerebral blood flow. The experiments outlined in this aim will elucidate the precise mechanisms through which cEC Ca2+ signaling is translated into the changes in blood flow, and will explore the hypothesis that cEC electrical and Ca2+ signaling mechanisms work cooperatively to finely tune brain blood flow. Aim 3. To elucidate the disruptive effects of chronic stress on capillary-to-arteriole communication. Here, we will use established rodent models of stress to explore the hypothesis that capillary function is perturbed by stress through mechanisms that impinge upon the normal sensing and responding of cECs to neural activity, thereby disrupting the electrical- and Ca2+-mediated control of local blood flow, and explore strategies for prevention and restoration.